Not applicable.
This invention is in the field of integrated circuit manufacture, and is more specifically directed to chemical bath integrated circuit wafer cleanup operations.
Chemical bath cleanup operations have been utilized in the manufacture of integrated circuits virtually since the inception of the field. Such cleanups are primarily useful in the removal of particulate and film-like residue that are generated as by products of various stages of the manufacturing process. In particular, chemical bath cleanups are typically used after a masked etch process to remove the masking material, typically photoresist, to remove any particulates or films that are generated as a result of the etch process itself, and also to remove metallic contaminants that can degrade device performance. Chemical bath cleanups are also used to remove native oxide films prior to the deposition (or thermal growth, in the case of a gate oxide) of a film, to promote adhesion of the new film to the underlying layer; such native oxides may be formed in previous processes, or even simply during the storage of the wafers in air between processes.
Typically, the chemical bath itself consists of a chemical solvent or reagent for the material to be removed. For solvent cleanup, the solvent may be a general-purpose solvent, such as deionized water, isopropyl alcohol, other organic solvents, and the like, for removing a wide range of residues that may be present. At other stages in the process requiring a reagent cleanup, a reagent will be specifically selected to remove a particular residue that is expected at a process station; examples of such cleanup reagents include dilute acid or base solutions (e.g., HF and NH4OH). Additionally, a sequence of cleanups in different chemical baths may also be performed, with a final chemical bath of deionized water or IPA to remove residue from the previous cleanups.
In recent years, new materials have been used in the manufacture of integrated circuits, particularly in carrying out masked etch operations of sub-micron features. However, the residues of some of these new materials have been observed to be resistant to removal by way of chemical bath cleanups. Examples of these materials include photoresists responsive to xe2x80x9cdeep-UVxe2x80x9d wavelengths of light exposure and new anti-reflective coatings that are applied below photoresist layers (so-called xe2x80x9cbottom anti-reflective coatingsxe2x80x9d, or xe2x80x9cBARCsxe2x80x9d), each of which have been observed to leave stubborn polymers behind after etch processes. Additionally, residues from modern highly active plasma etch chemistries have also been observed to be particularly persistent.
A conventional technique for improving the efficacy of chemical bath cleanup is to insert a physical action into the cleanup. One conventional example of such physical action is the injection of an inert gas, such as nitrogen, into the chemical bath to bubble the liquid; the bubbles of the injected gas provide a physical action in the chemical bath which can dislodge particulate and film residue from the wafer being cleaned. Another conventional approach applies ultrasonic energy to the chemical bath, resulting in a physical turbulence in the liquid that also dislodges such contaminants from the wafer. Such physical action has been observed to be quite effective in cleaning the integrated circuit wafers. Additionally, it is known that bubbling of the chemical bath can assist in keeping clean the walls of the tank containing the liquid chemical bath.
However, the physical action caused by the bubbling or ultrasonic energy has been observed to have detrimental effects on the eventual cleanup. In particular, the physical action produced by bubbling and ultrasonics causes turbulence at the surface of the bath, which has been observed to leave xe2x80x9cwater marksxe2x80x9d on the surface of the wafer as the wafer is inserted into and removed from the chemical bath. The nature of these marks depends upon the process step and chemical bath that is used. One type of water mark is in the form of an oxide growth stain, such as has been especially prevalent following an etch of doped polysilicon; such stains can locally change the reflectivity of the wafer, thus causing an error in a subsequent photolithography operation. Such oxide stains can also locally retard a subsequent etch, particularly of highly selective etches commonly used in modem integrated circuit manufacture, often resulting in failed or resistive contacts. Another manifestation of such a water mark results from a bubble that remains on the surface of the wafer during cleanup and prevents the chemical bath cleanup from cleaning residue from the portion of the wafer under the bubble.
Particles have also been observed to be trapped at the wafer surface as a result of withdrawing the wafer from the chemical bath during bubbling. It has been observed that extremely small particles, generated from the edges of the wafers, tend to collect upon bubbles at the surface of the chemical bath. When a wafer is withdrawn from the chemical bath through these particle-bearing bubbles at the surface, the particles will be transferred to the surface of the wafer, providing localized contamination.
Heretofore, integrated circuit process engineers have been faced with the difficult choice of either eliminating the physical action of the chemical bath cleanup operations, by permanently turning off the gas bubbling or ultrasonic energy, or of simply living with a certain level of watermark staining and other defects.
By way of further background, U.S. Pat. No. 5,698,040, commonly assigned herewith and incorporated by reference hereinto, discloses a known wafer cleaner and operation of the same.
It is therefore an object of the present invention to provide a chemical bath cleanup that utilizes physical action in combination with the chemical bath, while preventing watermark stains on the wafer upon insertion and removal.
It is a further object of the present invention to provide such a chemical bath cleanup that may be readily implementable into manufacturing process equipment.
It is a further object of the present invention to provide such a chemical bath cleanup apparatus that can use physical action to clean its chamber walls when no wafers are present.
It is a further object of the present invention to provide such a chemical bath cleanup apparatus in which the physical action enables a reduction in the cleanup time required.
Other objects and advantages of the present invention will be apparent to those of ordinary skill in the art having reference to the following specification together with its drawings.
The present invention may be implemented into a chemical bath cleanup, either a single wafer cleanup or a batch cleanup, by way of a programmable controller applied to the generation of physical action, such as a gas bubbler or ultrasonic transducer. The programmable controller is programmed to provide the physical action to the chemical bath while the wafers are present therewithin, and to then turn off the chemical bath for a waiting period prior to withdrawal of the wafers from the chemical bath. According to another aspect of the present invention, the programmable cleanup bath is programmed to generate the physical action for a selected time when no wafers are present therewithin. This operation is either programmed to occur periodically, or upon detection of a sufficient number of contaminants in the bath itself. The physical action assists in the self-cleaning of the sides of the bath vat.